1. Field of the Invention
The present invention relates generally to a sheet mesh for holding samples for examination by TEM (Transmission Electron Microscope). Specifically, the present invention relates to a method of processing such sample material utilizing the sheet mesh for supporting the material during processing.
2. Description of the Prior Art
For appraising the minute structures of modern semiconductor devices, a cross-section of the elements of such devices must be examined under high magnification, generally by way of a transmission electron microscope (TEM) or the like. Referring to FIGS. 14(A)-(D), a conventional method of processing sample material for such a process will be explained in detail. First, referring to FIG. 14(A), first and second substrates 1, 1 have membranes layers 2, 2 applied to one side thereof respectively. The first and second substrates 1, 1 are arranged such that the membrane layers 2, 2 thereof face each other and are joined therebetween via an adhesion layer to form a block of sample material a. Then, a thin wafer of the sample material a is cut from the main block, such that the membrane layers 2, 2 and the adhesion layer 3 run lengthwise substantially through the center of the sample material a. The sample material a is then attached to a rotatable polishing apparatus 4 via a bonding layer 5. The surface of the sample material a is then exposed to a polishing powder 6 under pressure applied from the opposite side by the rotatable polishing apparatus 4, as seen in FIG. 14(B) such that thickness of not more than 20 .mu.m is achieved and both sides are given a mirror finish.
Then, for processing of the sample material, as seen in FIG. 14(C), the wafer of sample material a is placed over an opening 7a provided in a single hole mesh 7 (sheet mesh) formed of a metallic sheet material and having a thickness of 10 um, for example. Referring to FIG. 14(D), the sheet mesh 7 with the sample material a thereon is mounted on a rotation apparatus 8 and is then rotated under vacuum conditions while being irradiated by a high pressure electrical discharge, as for example an Ar.sup.+ ion beam B, at an irradiation angle of 9.degree.-20.degree.. Irradiation is continued until a small hole is formed in the center of the wafer of sample material a, and at this, a finished sample for use with a transmission electron microscope is completed.
According to such conventional processing of sample materials for transmission electron microscopes, as seen in FIG. 15, when irradiation is carried out, the beam B is reflected by corners and edges of the openings 7a of the sheet mesh 7. This causes turbulence in the ion flow irradiating the sample material and, as seen in FIG. 16, a circumference of the small hole formed in the sample material a may receive insufficient irradiation, or unevenness and/or pitting may occur in the finish of the irradiated surface, degrading sample quality.
Further to this, the efficiency of the adhesion layer 3, used to bind the sample material a together, is dependent on the qualities of the membrane layers 2, 2. Thus a problem in which sufficient irradiation may not be obtained due to degradation of the adhesion layer is present. Also, under such conditions, lifting of Al, or another material forming the sample material a may occur.
Utilizing the above method, examination of an object to be observed by a transmission electron microscope, the membrane layer 2 for example, which must be positioned over the opening 7a of the sheet mesh 7, becomes difficult. Referring to FIG. 17(A) a condition is shown in which the positioning of the wafer of sample material a has slipped relative the surface of the sheet mesh 7 resulting, as seen in FIG. 17(B) in insufficient irradiation being applied to the portion to be examined, that is the membrane layers 2, 2.
Thus it has been required to provide a method for processing sample material for use with transmission electron microscopes in which optimal irradiation characteristics are provided during preparation of sample material. Also, a processing method is required in which positioning of the sample material is reliably assured and in which the adhesion characteristics between layers of the sample material are efficiently maintained.